Tennessee power plants have landed the state on a list of the top 25 producers of greenhouse gas emissions from carbon dioxide, according to a report released Wednesday.

The state ranked No. 21 for the emissions of the greenhouse gas that has been under scrutiny in recent months by federal regulators, according to the report by Ceres, a sustainable energy advocacy group.

The U.S. Environmental Protection Agency is expected next week to release new guidelines to curb carbon emissions at existing power plants. It's part of a two-step process that the Obama administration is taking to stem climate change. Last September, the EPA announced limits on carbon emissions for new plants.

Tennessee fared slightly better in the most recent report compared with the one released a year ago, in which the state ranked 19th.

And since 2007, the state's carbon emissions have dropped roughly 30 percent, said Christopher Van Atten, a vice president at M.J. Bradley & Associates LLC, which wrote the report.

"The primary reason for the decline was a switch from coal to natural gas," Van Atten said in an email.

While some industry observers have warned of job losses and reduced economic activity as a result of the EPA's new carbon rules, Ceres President Mindy Lubber said electricity producers have always found ways to innovate and meet stricter standards.

"The power sector can successfully meet air pollution standards while keeping our lights on," Lubber said. "There's no reason to think it can't do the same with carbon dioxide."

Electricity producers across the country have been able to cut carbon emissions 13 percent between 2008 and 2012, Lubber said.

Tennessee power providers put state among top carbon emitters

The state ranked No. 21 for the emissions of the greenhouse gas that has been under scrutiny in recent months by federal regulators, according to the report released by Ceres, a nonprofit energy research group.

"The power sector has already begun to de-carbonize through increased investment in natural gas, renewables, and increased efficiency," Lubber said.

While Ceres has produced the report since 1997, Lubber said attention to air emissions has grown in recent years.

"We've never released it at such a critical and opportune time," Lubber said in a conference call.

The report drew a straight line between carbon pollution and electricity production at coal-fired power plants. The Tennessee Valley Authority, the state's largest electricity producer, ranked fifth in both overall coal electricity production and emissions of carbon dioxide.

"As the supplier of electricity for 9 million residents in the Tennessee Valley, we recognize our responsibility in this area," TVA spokesman Jim Hopson said in an email. "This is a key reason why TVA is pursuing a diversified portfolio of power generation sources that increasingly relies on carbon-free power from nuclear energy, hydroelectric production, renewable sources such as wind and solar and energy efficiency, as well as cleaner burning natural gas."

The federal utility is amid a $1.1 billion project to cut certain emissions other than carbon at its coal-burning power plant near Gallatin by as much as 96 percent.

Despite ranking in the top half of states for total carbon emissions, Tennessee's coal plants looked more favorable when comparing emission rates. In that list, the state was 32nd. Meanwhile, comparing emissions rates of all fossil energy produced, the state ranked 16th.